Modern Warfare 2 has made about a bazillion dollars so far around the world, but that's not all profit. You've got to subtract the game's development costs. And for such a polished game, those must be pretty high...
And they are. An LA Times report on the game's launch says the game "cost $40 million to $50 million to produce". That's, uh, a lot for a game that's built atop a preceding title. Gran Turismo 5 has cost $60 million so far, but that game's been in development for five years, not the two it took to get MW2 out the door.
So, yes, if you were wondering how Activision got so much detail, Fiddy and Keith David into the game, that's how they did it. By throwing money at it.